Sunday, 23 October 2016

Lurking beneath the windows

Sometimes you embark on a course with one reason to the fore but end up sticking with it and rationalising it for other reasons.  Insulation and winter comfort had been the primary concerns driving the idea in late '15 of disturbing upstairs with building work. 

If asked now whether that work (which was more extensive, expensive and painful than I had bargained for) was needed or worth it, I would rationalise it on different grounds.  I now see it as enabling a healthier atmosphere better able to regulate humidity in the bedrooms upstairs - breathing walls, fireplace ventilation restored to two bedrooms etc.  I do also think the bedrooms will feel warmer than when their walls were entombed in cement but I couldn't quantify or prove this.  The final validation of the decision to bring the kangos into the bedrooms was a nasty surprise that got revealed when we did: some of the upstairs floor joists were rotting under areas of cement!
We knew from the work done in 2014 that the one wall in the house - top to bottom - which hadn't been cement plastered internally was the south facing front wall.  We think this was because it bowed slightly and cement-loving bungalow builders 15 years ago liked their straight lines and so built a straight stud wall covered with a light cement skim.  We had peeked behind it in '14 when popping the windows out for repair and thought it would be a simple matter of taking down the stud and then lime plastering the wall behind.  Had I looked closely behind the radiators under the windows (or just knocked on that section of wall), I might have realised that it wasn't all stud.

Internal view of south-facing front wall in one of the bedrooms

2014... in the process of popping out the windows revealing the stud walls

Sometime in April, I got a call at work from Kevin who was ripping out the stud:  'John there are poured cement sections of wall under the windows - do you want them kangoed out as well?'.  My answer was yes.    There then followed the call with the bad news: 'John the joists under the poured cement are rotten'.

As Kevin pointed out to soften the bad news, the positive thought was that we were discovering this now rather than 10 years later when it would be much worse.  So what to do?  First, understand why they rotted.  Then agree a fix which we would be confident would not risk recurrence.  As usual I turned to Pete Ward for advice.

Why they were rotting was fairly easy to deduce.  Rain from the prevailing southwesterlies was getting in through micro cracks in the old external cement render and getting trapped between the thin section of stone wall under the window and the poured cement wall on which the internal window cill sat. Some was probably also dripping down from the internal window cill having been driven in under the lower sash window and up over the base of the window frame (hard to believe but I'd witnessed it happening myself during wet winter Atlantic gales) and pooled on the window cill.  Once the moisture was caught behind the poured cement wall there was no way for it to evaporate internally and the joist ends were left sitting in constant damp cement and rubble.

I was pretty comfortable that the cause of the rotting would not persist given the work that had been (and was being) done to make the walls of the house breathable inside and out.  Also, the windows had been re-inserted after repair back in '14 sittin up on stone upstand slips that Kevin had cut and put in place to create a proper drip gap under the window frame  - rectifying something which hadn't been there previously.
But what were we to do to repair the rotting which had taken place?  The builders has seen injection treatment of joist ends tried in other cases.  Pete however was very clear: no wasting effort on chemicals, just get timber dry and support joists by picking them up and holding them into the wall.  Steel flitch plate or steel shoes were both options.  In the end, because the rotting was very localised to the end of the joists and the joists themselves were only 15 years old and supported by other unaffected floor joists,  we just doubled them up at the end by bolting with stainless steel bolts a metre of new joists alongside.  The main casualty was a metre depth of bedroom floorboards.

Just to make absolutely certain that these joists sit in future cleanly on dry stone with nothing but air around them, we will this winter (following Pete's advice) come at them from the ground floor and clear out any remaining rubble and concrete at their base and leave them lying cleanly on stressline concrete lintels.

And to replace the poured cement wall?  We considered a number of options for breathable insulating layers to fill out the very thin stone wall sections under those windows - including expanded cork board with lime plaster.   In the end we thought: why not use the leftover sheep's' wool (from the attic insulation) packed behind simple wooden window front boards?

Of course, a wooden board is only breathable if you don't slap acrylic or other synthetic paint on it.  And breath-ability would continue to be important here.  I am fatalistic that windows facing Atlantic gales full brunt will ship some water no mater what you do.  And winter rain lashing against lime render on a thin section of wall will lead to periods when most, if not all, of that thin wall will be damp - until the same strong winds dry the wall out through evaporation.  Cue conversation with carpenter:
'Have you ever used linseed paint? No.'
'Are you willing to try it if I get you some?  Yes'

The good news was that  - unlike the never ending saga of trying to dry the linseed paint on hard teak window frame wood from which acrylic paint had been partialy chemically stripped  in 2014 - the linseed paint actually dried pretty easily this time.  Why?  Firstly it was new untreated wood (maple) more receptive to absorbing paint (including a primer coat that was 50% oil).  Secondly, the carpenter happened to have a drying cabinet that featured both UV lamps and blown airflow - perfect for linseed paint!

Next post: I'm not sure yet but plenty still to do!




Saturday, 16 July 2016

Kangos upstairs

The previous post dealt with how the decision to have the internal cement plaster taken off the stone walls upstairs arose.  Although it didn't at the time influence the decision-making (perhaps it should have),  it is worth also mentioning an issue which I had begun to notice in 2015 as it had gradually built up (I'm not the most observant of people).  Wooden doors, bannisters and mantelpieces upstairs (painted in non-breathable acrylic paint) were accumulating a black mould.

This was not happening to doors downstairs (where almost all cement had been removed).  For a time I was mystified about this and later inclined to think it solely due to insufficient vapour extraction from the upstairs bathrooms.  I now think the lack of internal breathability of any of the upstairs walls must have been at least partly the issue.  Although it wasn't a driver of the decision to remove the concrete when that decision was taken, I hope and expect this issue will not recur in future now the upstairs walls are breathing.

Fast forward to March.... out goes all the bedroom furniture to be stacked in a covered pile in the sitting room and in comes protective hardboards for the flooring (fingers crossed - they're still in place at time of writing) and the kango hammers.  The ensuing mess and cloud of dust was in some respects the hardest of the several phases I've experienced with this rolling project.  There was no sanctuary this time.   Visiting involved airbnbing in the locality.

At one stage it was literally crawling between rubble and scaffold bars to get upstairs

One of the 2 previously covered fireplaces plus the original back window from before the addition of the mid C19th annex

The mid C19th annex upstairs with the other rediscovered fireplace

While the destruction phase was going on my main job was to decide on the lime plaster to go onto the walls.  Needless to say, I (over)analysed the options and probably tried the patience of Kevin and Pat in the process.  The suggestion had been to use Secil Ecocork which is a significantly breathable lime plaster system from Portugal which has some insulating properties in addition to its breathability.  This product seems to have achieved a broad degree of acceptance within the community working with lime in Ireland in recent years.  It is frequently used on stone walls with what seems a good track record to date.

A couple of months earlier, at the same time as the work on the attic, it was used in two small areas downstairs which I asked Pat and Kevin to work on as an 'experimental canvass' - a porch area out of which I was moving a boiler and the dank and windowless small toilet in the north east corner of the house.  I had been satisfied with the results to date.

External walls of porch plastered with Secil Ecocork plaster system

On the other hand, the plastering job to come upstairs would probably be the largest order for internal plaster I would make ever and I wanted to try and make sure it was fully thought through. Do it once and try not to have regrets later!

I struggled a little because there is a whole world of internal lime plasters and it can be confusing for the uninitiated to find their bearings.  I researched online, sent a question out to a LinkedIn building conservation group, asked Pete Ward and gradually concluded there were 2 broad options:
1) hydraulic lime mortars (plasters which set faster and harder giving more strength but as a tradeoff are somewhat less porous depending on the natural hydraulic lime 'NHL' strength of the makeup) 
2) non hydraulic, 'fat' or 'soft' lime plasters (which have a much slower set and give you a softer-looking plaster with maximum breathability)

The hydraulic lime mortars, because of their strength, are used for almost all outdoor lime rendering and had been used by Kevin and Pat in 2014 on the external lime rendering of my house (an NHL 3.5 mix in that case).   They are also often used for internal plastering and the Secil Ecocork is is a pre-mixed hydraulic lime plaster system - this is arguably part of its success in terms of uniformity of resulting performance and lower risk in application.

For me, if I was going to undergo all the destruction of removing cement, then I wanted to replacement lime plaster to have maximum breathability - why settle for less?  The reason why you might settle for a little less breathability is that hydraulic lime plasters with added aggregate (for example cork) can have slightly higher insulating characteristics than a soft lime plaster.  As far as I could glean, strength of plaster and/or insulating properties come at the expense of ultra-breathability.

Given this trade-off, Pete Ward's observation that the thermal mass of 2ft-plus thick solid walls constitutes  your real insulation was the cardinal point to bear in mind.  One of the other contributors on the linkedin conservation group put it nicely: 'the (thermal) specification of a few mm of inner wall covering is not going to make much difference one way or another. Re vapour permeability - go for the most porous, as the walls should be able to act as moisture reservoirs - dependent on environmental conditions'

Once I had that direction, the decision became easier; I considered asking Kevin and Pat to add lime putty to the Secil Ecocork system to take it down from NHL3.5 (I believe, although its hard to tell from the product literature) down to something like a very breathable NHL2.  In the end though, given I wasn't under any time pressure and could take time for plaster to set, I opted for the ultra-traditional choice for internal plaster on these islands; soft lime hemp plaster.

Soft lime hemp takes patience in application and then in waiting before it can be painted. To give an idea, the application of coats started in the second week of April and Kevin and Pat were still being cautious about painting one section of plaster on a shaded east facing wall late in June.

Time and performance (i.e. breathability) will be the test of the success or otherwise of this plaster choice.  The initial result however, from an aesthetic viewpoint (I write this as the furniture begins to go back into the bedrooms) is very pleasing - a plaster with an soft-edged organic look and feel to it.

Final coat beginning to dry in May

Fat lime plaster can give pleasing organic shape to corners

Next post:  a nasty surprise uncovered ...


Saturday, 11 June 2016

Upstairs inside walls - to leave under cement or not?

Alongside the insulation of the attic which proceeded at pace during January, the knotty issue of what - if anything - to do with the cement-plastered inside of the external walls upstairs was decided during that month.  As usual, the decision required me to spell out what I was looking to achieve (bedrooms that could feel warm and retain heat even in winter cold snaps) followed by an examination of the options with Pete Ward and Kevin+Pat at Midwest Lime to see if any option represented an improvement worth the investment.  In the end, this process led me to question and alter what I was looking to achieve as I learned, understood and thought more.

By now, the interior of the house upstairs was (apart from the fitted kitchen area) the last remaining substantial zone of cement plastering.  The work in 2014 had first prioritised the external rendering and then removal of cement from downstairs interior  (creating a ground floor internal 'evaporation zone' for the rubble stone walls).  Through all the building works, upstairs had been the refuge - no dust, continuously furnished, functioning radiators etc.

However, I always had a nagging unease about leaving upstairs as it was - combined with no appetite to extend cement hacking and dust clouds into our bedrooms.   At the back of my mind the answer from the conservation architect during his one hour verbal on-site consultation in Sept 2013 still echoed:
Me: 'how much cement needs to come off eventually?'
Conservation architect: 'ultimately - ideally and if possible - all of it should come off..... even if not all of it may need to be removed to fix the current damp problem'

Also gnawing at the back of my mind was awareness that cement-plastered walls can feel cold and although recent winters since I acquired the house had been relatively mild, I knew that the previous owner had found some of the bedrooms - in particular the one above the kitchen in the C19th annex which had 3 external walls - chilly during the more epic winters like 2010/11.    

I spent January exploring what insulation might be possible to retro-fit onto the cement plaster on the internal side of the external bedroom and upstairs landing walls.  I vaguely imagined some sort of insulating panels that could be fixed on and lightly plastered over with relatively little destruction.

Because I was looking to retrofit insulation onto an non-breathing internal cement plaster, my research started off seeking to establish whether, logically, it made no odds if that insulation was breathable or not.  In other words, was there any need to go for more expensive breathable insulating boards like Gutex or Calsitherm.

So what did the initial research (through online reading and calling suppliers) teach me and the builders?:
1) Even if retrofitting insulation onto cement, it did matter that this insulation be breathable.  Otherwise warm internal air would condensate when it hit the cold cement and (because it wouldn't be able to pass through the cement or back out through the insulation)  moisture would be trapped between the insulating board and cement ... a worse state of affairs than the status quo
2) Not not only did it matter that the insulation be breathable, it needed to be highly breathable - the highest spec available, which meant Calsitherm or its equivalent.  Gutex would not be breathable enough in this particular circumstance up against cold cement.

And this was the point at which the scope of what was on the cards for upstairs changed radically.   Calsitherm and its equivalent highly breathable calcium silicate insulating boards are not cheap, currently at least.  The cost estimate for material and labour to retrofit this onto the cement plaster was approximately the same as the cost estimate for putting hardboards down upstairs, hacking off the infernal cement altogether and replastering with lime.

So - not quite appreciating what the reality of losing the bedrooms and extending the cement dust cloud upstairs would prove to be like - I opted for 'so long cement, miss you not'.  

Next post: Kangos upstairs...

As this has been a shamefully photo-less post, some gratuitous unrelated before-and-after which may not make it into another post. One of the side jobs I'd asked Pat and Kevin to do while onsite was scooping out the infilled inglenook in what had once been the kitchen prior to the adding of the c19th annex:

Again, huge credit to Pete for guiding us on this and explaining breadovens!

 This ....

Became this .....

Then later this .....

And is now this ......